1. Field of the Invention
The present invention relates to a cutter blade for a mower which is driven to rotate about a vertical axis inside a housing.
2. Description of the Related Art
The cutter blade described above generates a wind inside a housing by a wind generating portion, so that this wind raises grass for facilitating its cutting or conveying cut grass. Incidentally, by enlarging the wind generating portion, it is possible to increase the amount of wind generated for enhancement of the ability to raise grass or to covey cut grass. On the other hand, with this type of cutter blade, a negative pressure can sometimes be generated on the back side of the wind generating portion (on the rear side relative to the rotational direction of the cutter blade). And, generation of such negative pressure leads to generation of vortex at this negative pressure portion, which in turn tends to invite increase of noise. Conventionally, as an arrangement for preventing generation of a negative pressure on the back side of the wind generating portion, there are known cutter blades disclosed in e.g. Japanese Unexamined Patent Application Publication No. 2002-315418 and Japanese Unexamined Patent Application Publication No. 2005-312396. More particularly, Japanese Unexamined Patent Application Publication No. 2002-315418 and Japanese Unexamined Patent Application Publication No. 2005-312396 disclose cutter blades wherein a hole portion is provided at the wind generating portion for establishing communication between the front side of this wind generating portion (the front side relative to the rotational direction of the cutter blade) and the back side of the same. With these cutter blades, it is contemplated to enlarge the wind generating portion by allowing air communication from the front side to the back side of the wind generating portion via the hole portion formed in this wind generating portion and to eliminate the noise associated with a negative pressure at the same time.
However, with the cutter blades disclosed in Japanese Unexamined Patent Application Publication No. 2002-315418 and Japanese Unexamined Patent Application Publication No. 2005-312396, the hole portion can sometimes be clogged up with cut grass during use of the cutter blade. With occurrence of such clogging of the hole portion with cut grass, the communication of air from the front side to the back side of the wind generating portion is hindered, so that negative pressure cannot be avoided sufficiently, thus failing to achieve the expected noise prevention effect. In view of the above-described, there is a need for a cutter blade capable of reducing noise with maintaining the wind generation function by its wind generating portion.